Spread spectrum (SS) systems, which may be CDMA systems, are well known in the art. SS systems can employ a transmission technique in which a pseudo-noise (PN) PN-code is used as a modulating waveform to spread the signal energy over a bandwidth much greater than the signal information bandwidth. At the receiver the signal is de-spread using a synchronized replica of the PN-code. The receiver can include an adaptive filter, such as one embodied in the form of a rake receiver, that is used for parallel correlation (acquisition) and multipath mitigation (tracking) of a received spread spectrum signal.
A variety of multiple access communication systems have been developed for transferring information among a large number of system users. Techniques employed by such multiple access communication systems include time division multiple access (TDMA), frequency division multiple access (FDMA), and AM modulation schemes, such as amplitude companded single sideband (ACSSB), the basics of which are well known in the art.
In Spread Spectrum (SS) or TDMA-SS transmission systems a succession of short-duration bursts emanating from a number of different stations are presented to a demodulator. Each burst may contain data frames from one or more data channels. Furthermore, the data frames may be interleaved data frames. Each data frame (interleaved or otherwise) generally contains a sync word used by the demodulator for frame synchronization purposes. In addition, one or more data frames may contain known bit patterns or training sequences used by the demodulator to improve the quality of reception. In general the location of these training sequences within a data frame are known in relation to the location of the sync word. It will be appreciated therefore that the sync word must be rapidly identified by the demodulator.
It should be noted that data frame synchronization is required as well in non-burst communication systems, such as continuous or substantially continuous transmission systems.
It can be appreciated that using sync words can result in certain disadvantages being realized. As examples, the use of sync words can: 1) require additional data bandwidth; 2) decrease available payload data space; 3) introduce a susceptibility of the sync word to corruption by noise or jamming, 4) introduce a potential for false synchronization; and 5) require some amount of additional time for a demodulator to search for and correlate with sync word.
Therefore, it is desirable to provide a system and method for rapid synchronization of a received signal, such as one containing data frames, and, when desired, the locating of bit patterns, such as training bits, in real time, or near real time, with respect to demodulator functions.